WASHINGTON U.S. officials say the surviving suspect in last week's attack on the Boston Marathon has told investigators he and his brother were angry about U.S. wars in Muslim countries.

Two officials said that Dzhokhar Tsarnaev acknowledged the anti-U.S. motive while being questioned by investigators last weekend.

One official on Wednesday said Tsarnaev cited the U.S.-led invasions of Iraq and Afghanistan as the motive for the Boston attack. The official was briefed on the investigation by the FBI.

The other official is close to the investigation. Both officials demanded anonymity to talk about the ongoing probe.

Neighbors have described Dzhokhar's older brother, Tamerlan, as visibly angry about the wars in Afghanistan and Iraq.

Tamerlan, 26, and Dzhokhar, 19, are accused of setting off the two bombs near the finish line of the Boston Marathon on April 15, killing three and injuring 264 people. The elder brother was later killed in a police standoff.

Meanwhile, U.S. investigators are in contact with the bombing suspects' parents in southern Russia and working with Russian security officials to shed light on the deadly attack, a U.S. Embassy official said Wednesday.

The parents plan to fly to the United States on Thursday, the father was quoted telling the Russian state news agency RIA Novosti.

"What happened is a terrible thing, but I know that my kids have nothing to do with this," she told Britain's Channel 4 News. "I know it. I'm mother. I have- you know, I know my kids. I know my kids."

The U.S. team traveled Tuesday from Moscow to the predominantly Muslim province of Dagestan "because the investigation is ongoing, it's not over," said the official, who spoke to The Associated Press on condition of anonymity because he was not authorized to speak to the media. He would not specify how long the Americans planned to stay in Dagestan.

On "CBS This Morning" Wednesday, CBS News senior correspondent John Miller reported that the FBI legal attache assigned to the U.S. Embassy in Moscow has joined with the Russian security services, the FSB, to work on a joint investigation, tracking down people, retracing steps Tamerlan Tsarnaev took during recent trips to Chechnya and Russia and interviewing people.

"What they're looking for is two things: Was there a bombmaker, a bomb teacher, a bomb test that happened there?" Miller said.

In his questioning in the hospital, Dzhokhar Tsarnaev said they were self-taught and self-radicalized.

"But you don't take that at face value, so you go back over that trip," said Miller. "Remember the younger brother may not know what his brother did in the Russian trip because he didn't go."

Miller said a Muslim convert known to the Tsarnaev family only as Misha, who family members told the AP steered Tamerlan Tsarnaev toward a strict strain of Islam, probably wouldn't be the bombmaker or teacher. However, he may be the person who connected Tamerlan Tsarnaev with one.

"Those are exactly the kinds of leads they're running backwards," said Miller. "They want to talk to everybody he met on that trip."

Investigators are looking into whether Tamerlan Tsarnaev, who spent six months in Russia's Caucasus in 2012, was influenced by the religious extremists who have waged an insurgency against Russian security services in the area for years. The brothers have roots in Dagestan and neighboring Chechnya, but neither spent much time in either place before the family moved to the United States a decade ago.

Zubeidat Tsarnaeva spent from morning to early evening Wednesday inside the FSB building in Makhachkala, the capital of Dagestan, where she was believed to be speaking further to U.S. and Russian investigators.

Heda Saratova, a prominent Chechen rights activist providing support to the distraught mother, said Tsarnaeva first went in for questioning on Tuesday, returning late at night. Saratova said she had no details about the discussions, but Tsarnaeva said they were "cordial."

The father, Anzor Tsarnaev, also was summoned to the FSB headquarters but did not go because he felt ill, Saratova said.

He has said previously that he intended to travel to the U.S. this week to talk to police and seek "justice and the truth." The family has said that he wants to bring Tamerlan Tsarnaev's body back to Russia.